1. Field of the Invention
The present invention relates to inductors and methods of manufacturing the same.
2. Description of the Related Art
In a conventional inductor, a conductive film is formed by plating a film over the entire surface of an alumina ceramic member, and a spiral coil is formed by removing a portion of the conductive film via a laser to produce the inductor. However, in such an inductor, since the core is made of a non-magnetic material, a large inductance is not obtainable, resulting in large size inductors.
On the other hand, a small inductor is known, in which a thin conductive metallic layer is uniformly formed over the peripheral surface of a cylindrical magnetic core made of a magnetic material such as a ferrite, and a spiral coil is formed around the peripheral surface of the cylindrical magnetic core by trimming the conductive metallic layer via laser trimming (as disclosed in Japanese Unexamined Patent Publication No. 60-144922). In such an inductor, since the core is made of a magnetic material, a large inductance is achieved in a small size inductor.
When a conductive film is formed on the surface of a magnetic body and the conductive film is trimmed to define a spiral coil, on each end of the obtained spiral coil, the resistance of the magnetic body itself is connected in parallel to the coil. When an Nixe2x80x94Zn-based ferrite which has a high specific resistance is used, the resistance thereof is usually approximately 108xcexa9 to 1012xcexa9. When the conductive film is irradiated with a laser, the irradiation also reaches the ferrite layer under the conductive film. At this stage, since the ferrite layer is in a molten state an dissolves conductive components of the conductive film, the ferrite layer which originally had insulating properties becomes partially conductive. Consequently, a portion subjected to laser machining has a significantly decreased surface resistance, and the resistance of the overall magnetic body is decreased to approximately 102xcexa9. Such a resistance is connected to the coil in parallel.
Since coils usually have an impedance of 102xcexa9 to 103xcexa9, the resistance connected in parallel to the coil must be at least 10 times the value of the impedance. That is, a coil having an impedance of 102xcexa9 requires a resistance of approximately 103xcexa9, and a coil having an impedance of 103xcexa9 requires a resistance of approximately 104xcexa9. Thus, even if an Nixe2x80x94Zn-based ferrite is used, when a coil is formed with a conductive film by laser machining, a resistance decreases greatly, which is undesirable.
Furthermore, in addition to the resistances arranged in parallel to the coil, resistances are connected in parallel between each turn of the coil, and decreases in such resistances are also undesirable.
Accordingly, a method is known in which an insulating layer is formed by applying an insulating coating to the entire surface of a magnetic body, and a conductive film is formed on the entire surface of the insulating layer, and thus the surface of the magnetic body is protected so as to be not directly subjected to laser machining. With such a method, a decrease in the resistance can be reduced.
However, in the above method, variations in dimensions may occur during manufacturing process. That is, when an insulating layer is formed on the surface of a magnetic body, by immersing the magnetic body in an insulating liquid glass or resin, or by coating the magnetic body, variations in the thickness of the insulating layer are added to variations in the outer diameter of the magnetic body, thus increasing tolerances. Generally, inductance changes depend on the diameter of a coil. That is, variations in the thickness of the insulating layer cause variations in inductance.
When an insulating layer is provided on the surface of a magnetic body, the insulating layer merely adheres to the surface of the magnetic body. Thus, separation of the insulating layer may easily occur, resulting in more defects as well as a decrease in reliability.
To overcome the problems described above, preferred embodiments of the present invention provide an inductor and a method of manufacturing the same in which a decrease in the resistance of a magnetic body caused by laser machining is reduced, variations in inductance due to variations in the thickness of the insulating layer and the outer diameter of the magnetic body are greatly decreased, and problems such as separation of the insulating layer from the magnetic body are prevented.
The above advantages are achieved by preferred embodiments of the present invention.
In one preferred embodiment of the present invention, an inductor includes a bar-shaped ferrite core and a spiral coil. The spiral coil is formed by removing a portion of a conductive film formed at a location at least around the peripheral surface of the ferrite core. The surface of the ferrite core is impregnated or permeated with an insulating glass before the conductive film is formed.
In another preferred embodiment of the present invention, a method of manufacturing an inductor includes the steps of impregnating the surface of a bar-shaped ferrite core with an insulating glass via thermal melting, forming a conductive film at least around the peripheral surface of the ferrite core impregnated with the insulating glass, and forming a spiral coil by removing a portion of the conductive film with laser irradiation on the ferrite core provided with the conductive film.
When the portion of the conductive film is removed via the laser, although a portion of the ferrite is also melted by the energy of the laser, the impregnated glass is also melted to form a mixture region in which the ferrite having a decreased resistance and the insulating glass are mixed. The mixture region does not become conductive due to the high resistivity ratio of the glass, thus minimizing a decrease in the overall resistance. Since the surface of the ferrite core is impregnated with the glass via thermal melting, the glass is enclosed in the ferrite, and thus problems, such as variations in the diameter and separation are overcome. Additionally, the region of the ferrite core which is impregnated with the glass includes at least the region for forming the spiral coil, and it is not necessary to include the entire surface of the ferrite core.
In another aspect of preferred embodiments of the present invention, the content of the glass is preferably about 0.1% to about 20% by weight of the ferrite core. If the glass content is less than about 0.1%, the insulating properties is insufficient, and if glass content exceeds about 20%, the impregnation into the ferrite is degraded.
In another aspect of preferred embodiments of the present invention, the ferrite core may be an Nixe2x80x94Zn-based ferrite core. Although the Nixe2x80x94Zn-based ferrite core has a significantly high permeability and a high resistivity ratio, the Nixe2x80x94Zn-based ferrite core easily becomes conductive by being melted via laser irradiation, and thus preferred embodiments of the present invention are effective.
In another aspect of preferred embodiments of the present invention, preferably, the inductor includes a dielectric layer disposed partially or entirely on the exterior of the spiral coil, and a capacitor electrode disposed partially or entirely on the exterior of the dielectric layer. Thus, a capacitance is created between the spiral coil and the capacitor electrode via the dielectric layer. In such a case, a composite electronic component having inductance and capacitance is achieved.
Other features, elements, aspects and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the invention which refers to the accompanying drawings.